A wide variety of fuel systems for internal combustion engines are well known and widely used, with most modern fuel systems including a fuel injector for delivering metered quantities of a fuel to a combustion chamber. Over the past century, an almost innumerable variety of fuel injector designs have been developed responsive to various operating parameters and operating conditions in an effort to optimize engine performance and operation in one or more ways. Even today, innovation in this field remains robust as efforts to reduce emissions, amongst others, has given rise to new engineering challenges that have been the focus of much inventive effort. For example, the desire to reduce emissions has led to more precisely engineered fuel injectors designed to deliver consistent, accurate quantities of fuel in an effort to achieve cleaner, more reliable, and more complete combustion reactions.
In recent years, engineers have discovered that relatively high fuel injection pressures, and rapid, yet highly precise movement and/or positioning of fuel injector components can offer various advantages relating to emissions composition, efficiency, and other engine operating and performance parameters. Various efforts to reduce emissions and/or to increase performance have also contributed to relatively high operating temperatures within the fuel injectors. To operate optimally under relatively harsh conditions such as high temperatures, fuel injector components are often machined to tight tolerances. Excess heat is known to cause dimensional instability of the fuel injectors, potentially resulting in unreliable injector performance, and can additionally result in varnishing, lacquering, or other problems which typically has an adverse effect on injector performance as well.
One common strategy for addressing the problem of high operating temperatures involves delivering a cooling fluid, such as fuel, to the fuel injector such that some of the heat energy generated by the fuel injector is transferred to the cooling fluid. Such strategies may cause or increase the potential for fuel to become contaminated with particulates, which can cause obstruction of nozzle outlets in the injector, cause wear at the close tolerances of the injector components, or otherwise damage the injector or result in unacceptable injector performance.
Various strategies have been proposed for protecting fuel injector components from potentially contaminating particulates. Most of these strategies involve adding a filter to, or upstream of, the fuel injector. For example, U.S. Pat. No. 6,446,885 to Sims et al. (“Sims”) discloses a secondary filter assembly for a fuel injector. The filter in Sims is mounted on a needle valve assembly within the fuel injector, with the filter having a number of holes configured to arrest particulates of a certain size. While this and other strategies prevent contamination under certain conditions, there remains ample room for improvement and development of alternative strategies.